Chemical sensors can be defined as devices able to detect the presence and/or concentration of a certain group of chemicals or a specific substance. Sensors in which the detection of a certain substance occurs by color change have the advantage of an immediate visual analysis via visual observation, calorimetric methods or image analysis.
The technological improvement related to detecting and signaling the presence of at least one chemical compound has been developed to seek new chemical sensors that exhibit the characteristics of lower costs, short response time to a specific color change, reliability (eliminating the possibility of a false response) and higher sensitivity.
In this context, many chemical sensors have been prepared using the sol-gel technology. The sol-gel material provides high surface area, narrow pore size distribution and purity. The sol-gel acts as a sorbent material capable of sampling, retaining, concentrating and releasing compounds.
The international publication WO1993/04196 reports about a porous glassy structure containing a biologically active encapsulated material able to detect through photometric techniques the quantitative and qualitative presence of several organic or inorganic compounds, especially enzymes. However, that application does not describe that said porous glassy structure obtained presents good thermal stability and good mechanical stability.
The patent application US 2007/0161069 reports about the invention of biosensor compounds from complex Ruthenium compounds and an enzyme. The claimed product acts through the fluorescence of ruthenium compounds, which occurs in the ultraviolet (UV) region. Although the substrate used may be polymeric, the application does not mention that the biosensor obtained presents good thermal or mechanical stability; additionally, its response takes place in the UV region, which restrains its use as a sensor that is visible to the naked eye.
The international publication WO/2006/086197 A2 describes obtaining sensor elements used for measuring the concentration of gaseous substances from “cytochrome c” embedded in a sol-gel matrix. Once again, in that document, thermal and mechanical stability data for the sensor obtained are not described.
The patent application US 2007/0071789 introduces bio-active materials used for medical implants, which are formed by drugs encapsulated in a sol-gel reaction. The drugs are released to the organism for long periods at body temperature, data about this bio-active material at high temperatures or under mechanical strain conditions are not described.
Another patent application, US 2006/0154414, presents a sensor compound applied to the detection and removal of contaminants, such as pesticides and insecticides. In spite of the sensor's good thermal stability indicated in that application, their use is difficult when they are mixed in polyolefinic compounds due to the incompatibility between the sensor and the polyolefinic matrix.
The patent application US 2006/0172431 reports about a sol-gel encapsulated hexanuclear Molybdenum/Tungsten cluster, with 12 anionic ligands for in vivo and in vitro biological monitoring of the oxygen content. Substituted metallic structures, such as that of Tungsten used in this compound, show low thermal stability.
Finally, the patent application US 2006/0267094 presents a sensor for carbon dioxide ((CO2) and for a CO2/O2 combination and the use of this sensor in films composed by Terephthalate Polyethylene (PET), Polyethylene (PE) and PET/PE blends, by printing laminated films. Due to the low thermal stability, the sensor is applied to the film surface and, thus, acts as a sensor, which makes the packaging manufacturing process more complex, slower and more expensive.
Standing out among the most widely used sensors are those for detecting oxygen from both living and non-living organisms, in addition to sensors sensitive to organic compounds such as sugars and amino acids, among others. Usually, these types of sensors have neither thermal nor mechanical stability to be industrially processed.
On the other hand, the extreme conditions on which polymers are processed are well known, especially in what concerns temperature and shear forces. Therefore, if chemical sensors will be used as filler in polymer matrices, as suggested by the present invention, there are essential properties, such as high thermal stability at high temperatures, high stability to shear forces and good compatibility with the polymeric phase, which must be observed.
The sensors described in the prior art references mentioned above fail to present thermal and mechanical stability, particularly at high temperatures and shear forces, do not have characteristics which may favor their compatibility with polymers.
Accordingly, there was a need for sensors with good compatibility with polyolefin matrices, which improves its dispersion in the polymeric mass during processing and, consequently, provides better effectiveness for its sensory properties.
The sensor of the present invention presents good compatibility with the polyolefin matrix used and also thermal and mechanical stability. Therefore, they can be mixed with polymers by conventional extrusion procedures, which usually takes place at temperatures about 150° C.-300° C., without losing their activity. Such effect is indicated by a color change in the presence of amines and amides, as well as in the presence of any substance that may change the sensor's pH, such as, for example, oxide-reducing compounds and vapors thereof. In interacting with the sensor or with the sensor incorporated in a polymeric matrix, these substances make the sensor show a color change.
The state-of-the-art literature does not describe or suggest the subject matter described and claimed in the present application, since it does not present a thermally and mechanically stable chemical sensor with hybrid characteristics able to respond to pH changes in the presence of amine, amide and oxide-reducing compounds by changing color through direct contact and/or through the vapors thereof.
The sensitive polymeric composition containing the sensor of the present invention incorporated there into may be used in the food, pharmaceutical, environmental, petrochemical and analytical detection industries.